Conventionally known is a stroke simulator in a brake system for giving a simulative operation feel to a brake operation member by operating the brake operation member to compress an elastic member. See Patent Document 1 for example, Japanese Patent Laid-Open No. 2005-162127, incorporated herein by reference.
In FIG. 6 of Patent Document 1, there is shown a stroke simulator 14 including a control piston 90 having a cylindrical shape with a bottom, an intermediate transmitting member 171 provided at the bottom of the control piston 90 through a coil spring 168, an elastic member 167 having one end abutting against the intermediate transmitting member 171, and an input piston 166 abutting against the other end of the elastic member 167 and movably inserted in the control piston 90, the input piston 166 being connected to an input rod 170 provided on a side of a brake pedal as a brake operation member.
When the brake pedal is depressed, the elastic member 167 provided between the intermediate transmitting member 171 and the input piston 166 is compressed to give a simulative reaction force to the brake pedal.
A clearance is defined between the inner circumferential surface of the control piston 90 and the outer circumferential surface of the elastic member 167. In the case of increasing the simulative reaction force on the brake pedal to thereby obtain a hard operation feel, the clearance mentioned above may be reduced. Accordingly, the elastic member 167 comes into contact with the control piston 90 in an early stage of the stroke of the input piston 166, so that a hard operation feel on the brake pedal can be obtained.
However, after the outer circumferential surface of the elastic member 167 comes into contact with the whole of the inner circumferential surface of the control piston 90, the compression of the elastic member 167 is rapidly suppressed. As a result, the stroke of the input piston 166 is reduced and it is therefore difficult to ensure a predetermined stroke of the brake pedal.